Tower silos are used to store bulk materials and forage feeds for animals, such as silage and haylage. The silos are of two general types, i.e., (1) a top unloading unsealed tower silo, and (2) a bottom unloading sealed tower silo. Top unloading machines are used to remove material from unsealed tower silos. The top layer of the material must be timely removed to minimize the spoilage as the material is exposed to atmospheric air. The oxygen in the air promotes mold growth in the material.
Sealed tower silos are used with bottom unloaders to remove material from the bottom of the silo. These silos have air impervious side walls and treated side walls to minimize the leakage of air into the silo. The sealed silos limit the supply of oxygen in the silo, thereby reducing the spoilage of the silage. The sealed tower silos require substantial amounts of labor, time, and capital to construct.
Bag structures have been used with sealed silos to compensate for differences in the air pressure inside and outside of the silo. Deringer in U.S. Pat. No. 2,722,171 discloses a tower silo having a flexible bag for storing silage. The bottom end of the bag is attached to the silo wall. A cable and pulley arrangement is used to support the bag in the silo. The bag rests on top of the silage and is free to move downwardly as the silage is withdrawn from the silo with a bottom silo unloader. Osborne in U.S. Pat. No. 3,122,985 discloses a tower silo having an expandable bag to provide a roof for the silo. The bag prevents the escape of internal gases and entrance of the outside air into the silo.